Method for evaluating the bandwith of a digital link

ABSTRACT

The invention relates to a method for evaluating the bandwidth between a first point and a second point liable to exchange digital data packets in a telecommunications network including a plurality of sub-networks. The method according to the invention includes the following steps: for each transmission direction through at least one of said sub-networks, associating a same identifier with the quasi-simultaneously transmitted packets, time-stamping and recording the received packets, identifying and sorting the packets received with the same identifier, selecting the largest possible integral number m of groups of packets with the same identifier, measuring the time intervals separating the instants when the packets of the selected groups are received by the second point, calculating the bandwidth according to the number of packets of the selected groups and to said total transmission time of said packets.

TECHNICAL FIELD

The invention pertains to the field of telecommunications and morespecifically relates to a method for evaluating the bandwidth between afirst and second point liable to exchange data packets via a digitallink in a telecommunications network including a plurality ofsub-networks.

The invention also relates to a device for applying the method.

The invention finds application in telecommunications networks such asthe Internet network.

STATE OF THE PRIOR ART

A known method for evaluating the bandwidth in a telecommunicationsnetwork consists in transmitting from a first point of the network afile via FTP (File Transfer Protocol) including a time mark and inmeasuring the rate for receiving this file by a second point of saidnetwork. Transmission of a file with a large size via FTP in a linkgenerates an overload of the network. Moreover, as the load generated bythe users of the network at the instant of the measurement is unknown, atransfer of a file with a small size via FTP does not guarantee anoptimum use of the available bandwidth. All these factors causemeasurement of the file receiving rate and so, the available bandwidthupon transfer via FTP by the second point of the network, to beuncertain.

Another method known in the prior art, consists in measuring theabsolute transmission time for a data file between both points of thenetwork, time being measured at each point with the highest accuracy aspossible. Of course, this method is more accurate but has a high costinsofar that it requires the use of a time measuring system with highaccuracy at each end of the network, such as delivered by a GPS (GlobalPositioning System) type transmission system, for example.

The object of the invention is to overcome the drawbacks of the priorart as described above by means of a method and a simple low cost devicecapable of being used between any points of the network.

Another object of the invention is to isolate and unambiguously localizea congestion point when data exchanged between two points of a networktransit through several sub-networks.

DESCRIPTION OF THE INVENTION

The invention recommends a method for evaluating the bandwidth between afirst point and a second point including terminals liable to exchangedigital data packets in a telecommunications network including aplurality of sub-networks.

The method according to the invention includes the following steps:

for each transmission direction through at least one of saidsub-networks,

-   -   a. associating a same identifier with the quasi-simultaneously        transmitted packets,    -   b. time-stamping and recording the received packets,    -   c. identifying and sorting the packets received with the same        identifier,    -   d. selecting the largest possible integral number m of groups of        packets with the same identifier,    -   e. measuring the time intervals separating the instants when the        packets of the selected groups are received by the second point,    -   f. calculating the bandwidth according to the number of packets        of the selected groups and to the total transmission time of        these packets.

By identifying the quasi-simultaneously transmitted packets in the fluxtransmitted from the first to the second point of the link, one isplaced under the actual conditions of use of the network's users, underwhich estimation of the measured bandwidth reflects the actualcongestion of the link at the instant of measurement.

In a preferred embodiment, the bandwidth is calculated with thefollowing expression:$\overset{\_}{BW} = {\frac{1}{m}{\sum\limits_{j = 1}^{m}\left\lbrack {\frac{1}{n_{m}}{\sum\limits_{i = 1}^{n_{m}^{- 1}}\frac{l_{i,m}}{t_{{({i + 1})}m} - t_{i,m}}}} \right\rbrack}}$

wherein

-   -   li,m represents the length of the packet of rank i of the m^(th)        group of packets,    -   ti represents the time mark of the packet of rank i of the        m^(th) group of packets,    -   ti+1 represents the time mark of the packet of rank i+1 of        m^(th) group of packets,    -   n represents the number of packets of the m^(th) group of        packets.

To improve the accuracy of the evaluation, the method is applied on anumber of groups of packets larger than 1.

In a first embodiment of the invention, the evaluation of the bandwidthis performed on-line.

In a second embodiment of the invention, the evaluation of the bandwidthis performed off-line.

In a particular application of the invention the communications networkis of the IP (Internet Protocol) type.

The invention also relates to a device for evaluating the bandwidthbetween a first point and a second point liable to exchange digital datapackets in a telecommunications network including a plurality ofsub-networks.

This device includes:

-   -   means for marking the transmitted packets,    -   means for time-stamping the received packets,    -   means for sorting the received packets,    -   means for measuring the time intervals separating the instants        when the transmitted packets are received by the second point,    -   means for calculating the bandwidth.

SHORT DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent fromthe description which follows, taken as a non-limiting example, withreference to the appended figures wherein:

FIG. 1 schematically illustrates a digital line in a telecommunicationsnetwork in which the method according to the invention is implemented,

FIG. 2 is a block diagram of a module for analyzing packets according tothe invention.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

The invention will now be described in an implementation on the Internetnetwork.

FIG. 1 schematically illustrates a bidirectional digital link 1 betweena first terminal A and a second terminal B connected to a first localnetwork 4 and to a second local network 6 respectively and exchangingdigital data through a first sub-network 6 and a second sub-network 8according to the TCP (Transmission Control Protocol) mode or accordingto the UDP (User Datagram Protocol). First and second modules (10, 12)for marking data packets transmitted by terminal A (B, respectively) anda module (14, 16) for analyzing data packets received by terminal A (B,respectively) are laid out at each end of the digital link 1 betweenterminals A and B, respectively.

FIG. 2 schematically illustrates a block, diagram of an analysis moduleaccording to a preferred embodiment including an adaptation interface 20connected to the IP link 1 via a coupler 22, a module 24 for extractingdata packets from the link 1, a module 26 for acquiring said packets, amodule 28 for time-stamping extracted packets for associating a sametime identifier with a quasi-simultaneously transmitted group ofpackets, a memory 30 for storing the time-stamped packets, a module 32for sorting packets with the same time identifier, a selection module 34for isolating groups of packets with the same time identifier and thelargest number of received packets, a module 36 for measuring theinter-packet transfer time and a module 38 for calculating thebandwidth.

In operation, each of the A or B terminals, may simultaneously be atransmitter and a receiver. The exchanged data transit through thenetworks 6 and 8, the respective congestions of which at a given timedepend on the number of connected users. Marking of the packets isachieved following a request sent by the receiving terminal to thetransmitting terminal. It may be achieved by enabling the time-stampingoption described in the RFC 1323 standard for example.

To evaluate the available end-to-end bandwidth, the extraction module 24isolates the data packets transmitted during a very short time from thetransmitting terminal to the receiving terminal and transmits thesepackets to the time-stamping module 28 which associates a transmissiondate with each packet. The packets are then stored in the memory 30. Themodule 32 sorts the packets bearing the same sending date and transmitsthem to the module 34. The latter selects an integral number of groupsfrom the sorted groups including the largest number of packets andtransmits these groups to the measurement module 36 which measures thetime intervals separating the reception of different successive packets.The measured intervals are then transmitted to the module 38 forcalculating the bandwidth, which calculates on-line the bandwidth of thelink according to the total length of the analyzed packets and to thetransmission time of these packets.

To evaluate the available bandwidth in each sub-network, the analysis ofthe received packets is carried out by the third module 18 laid outbetween the sub-networks 6 and 8.

1. A method for evaluating the bandwidth between a first point and asecond point liable to exchange digital data packets in atelecommunications network including a plurality of sub-networks,characterized in that it includes the following steps: for eachtransmission direction through at least one of said sub-networks, a.associating a same identifier with the quasi-simultaneously transmittedpackets, b. time-stamping and recording the received packets, c.identifying and sorting the packets received with the same identifier,d. selecting the largest possible integral number m of groups of packetswith the same identifier, e. measuring the time intervals separating theinstants when the packets of the selected groups are received by thesecond point, f. calculating the bandwidth according to the number ofpackets of the selected groups and to the total transmission time ofthese packets.
 2. The method according to claim 1, characterized in thatthe bandwidth is calculated with the following expression:$\overset{\_}{BW} = {\frac{1}{m}{\sum\limits_{j = 1}^{m}\left\lbrack {\frac{1}{n_{m}}{\sum\limits_{i = 1}^{n_{m}^{- 1}}\frac{l_{i,m}}{t_{{({i + 1})}m} - t_{i,m}}}} \right\rbrack}}$wherein: li,m represents the length of the packet of rank i of them^(th) group of packets, ti represents the time mark of the packet ofrank i of the m^(th) group of packets, ti+1 represents the time mark ofthe packet of rank i+1 of m^(th) group of packets, n represents thenumber of packets of the m^(th) group of packets.
 3. The methodaccording to claim 2, characterized in that the number m is largest thanor equal to
 1. 4. The method according to claim 1, characterized in thatmarking of the data packets is achieved at the transmitting point upon arequest from the receiving point.
 5. The method according to claim 1,characterized in that the evaluation of the bandwidth is achievedon-line.
 6. The method according to claim 1, characterized in that theevaluation of the bandwidth is achieved off-line.
 7. The methodaccording to claim 1, characterized in that the telecommunicationsnetwork is of the IP type.
 8. A device for evaluating the bandwidthbetween a first point and a second point liable to exchange digital datapackets in a telecommunications network including a module for markingthe transmitted packets and a module for analyzing the received packets,characterized in that the analysis module includes: means fortime-stamping the received packets, means for sorting the receivedpackets, means for measuring the time intervals separating the instantswhen the transmitted packets are received by the second point, means forcalculating the bandwidth.
 9. A module for analyzing data packetsreceived in a telecommunications network, characterized in that itincludes: means for time-stamping the received packets, means forsorting the received packets, means for measuring the time intervalsseparating the instants when the transmitted packets are received by thesecond point, means for calculating the bandwidth.